High-tension cable to prevent a breaking down of the insulation



April 3, 192a. 1,665,191

E. G. SIEVERT ET AL HIGH TENSION CABLE TO PREVENT A BREAKING DOWN OF THEINSULATION Filed NOV. 9, 1925 a. 5M W Patented Apr. 3, 1928.

UNITED STATES PATENT OFFICE.

ERNST GUSTAV SIEVEBT AND HENNING SVE NSSON, OF SUNDBYBERG, NEAR STOCK-HOLE, SWEDEN.

HIGH-TENSION CABLE TO PREVENT A BREAKING DOWN OF THE INSULATION.

Application filed November 9, 1925, Serial No. 67,949, and in SwedenNovember 20, 1924.

The present invention refers to an improvement in high-tension cables toprevent a breaking-down of the insulating layer.

Such a breaking-downwill generally take place in suchpoints of thecable, in which the insulating power ofthe layer has been reduced, forinstance by a somewhat less thickness, already at the manufacture, orhas got any other unintentional reduction of the specific electricinsulating power of the insulatin material. If a puncture has oncehappened in some point of. the insulating layer the cable will be Veryrapidly destroyed as the puncture is combined with chemical as well asthermal processes which exert influence upon adjacent parts of theinsulating material and which will gradually cause a .totalbreaking-down between the very conductor of the cable and the earth.

According to this invention, in order to remove this source ofdisturbances, one or more layers of an insulating material, having anelectric insulating power inferior to the remaining insulating material,are applied 2 into the insulating layers of the cable.

This arrangement efi'ects an equalizing of the tension, by which factthe causes of the initiating of the partial puncture are removed or atleast, essentially reduced. It is evident that the equalizing tensionwill be the better and more complete thelower the electric insulatingower of the equalizing layer is. On the ot er handa reduction of thespecific electric insulating power of said venience or danger dependingupon the fact that if the electric insulating power of the layers ismade too small, two partial unctures possibly produced, in spite oi theequalizlng layers, at a distance from one another counting in thelongitudinal direction of the cable, may add so thatthe result will'beinferior to that obtained without any equalizing layer or layers. Theelectric insulating power of the equalizing layers should, on account ofthis, accordin to the invention, also be chosen with regar to theprobable distance between weakened points, favorin the arising ofpartial puncture, of the ins ating material in a well made cable,

equalizing layers involves another incon-v a weakened point 10, thetension will -maintain the maximum potential difference between twobreaking-down points l0cated"65 in the equalizing layer, provided thesepoints are not located at a shorter axial distance than the probableminimum distance supposed in advance, which, as already indicated above,is different for diiferent cablb structures. As insulating materials forthe equalizing layers, a plurality of "difi'erent materials, known perse, may, of course, be used, for instance asbestos, which material hasproven to be particularly suitable.

The annexed drawing shows, diagrammatically, an embodiment of a cableaccording to the present invention, in longitudinal section.

1 is the lead sheath, 2, 3, 4, 5 the several layers of insulatingmaterial, 6, 7, 8, 12 the equalizing layers' placed between the formerand 9 the electric conductor.

If, for instance, the insulating layer 2 at the outside, whenmanufactured, has got 1ncrease at this point, but on the other hand theequalizing layer 6 tends to reduce the tension and equalize it so as toreduce the danger of a breaking down. In the same 99 manner theincreasing of tension, due to 'a ossible weak point 11 in theinsulating. ayer 3, is equalized. If, in spite of this, the points 10and 11 should be punctured, these unctures are, however, prevented fromaddmg by the relatively low electric insulating power of the equalizinglayer 6, said equalizmg layer preventing (the example chosen being stillconsidered), the voltage drop produced in thepoint 10 from beingtransmitted to the point 11, which is supposed to ed, between adjacentweakened points in the insulating layers 2 and 3.

Having now particularly described the nature of our invention and themanner of its operation, What we claim is:

A high-tension cable including an insulat- 10 In testimony whereof weherewith aflix 15 our signatures.

ERNST GUSTAV SIEVERT.

HENNING SVENSSON.

